Laura Robson hits a return to Stosur during their singles match at the U.S. Open Credit: Gary Hershorn / Reuters

Laura Robson's U.S Open quest has been ended by Australia's Sam Stosur, who won in straight sets.

Stosur needed nine match points to finally end Robson's run, winning 6-4, 6-4. The seventh seed closed out the match when she came in for a ball that ticked the net and knocked an unreturnable shot deep to Robson's forehand.

Robson, who had previously knocked out four-time Grand Slam titlist Kim Clijsters and 2011 French Open champion Li Na, tried to get back in the match after falling down 5-2 in the second set, but her 41 unforced errors turned out to be too much to overcome

Britain's Laura Robson pulled off the biggest win of her life at the US Open to bring Kim Clijsters' professional singles career to an end.

Three-time champion Clijsters announced earlier in the year this tournament would be her last and, although she still has doubles to come, there will be no fairytale fourth singles title.

Robson, 18, had never won more than one match at a grand slam before but found her best form on the biggest stage to triumph 7-6 (7/4) 7-6 (7/5) and reach the third round, where she will play ninth seed Li Na.